The present invention relates to acoustic ink printing. It finds particular application in conjunction with producing higher pixel resolutions from an acoustic ink printhead and will be described with particular reference thereto. It will be appreciated, however, that the invention will also find application in correcting directionality errors for droplets produced by acoustic ink printers, and the like.
Various fluid application technologies, such as printing technologies, are being developed. One such technology uses focused acoustic energy to eject droplets of marking material from a printhead onto a recording medium.
Acoustic ink printheads typically include a plurality of droplet ejectors, each of which launches a converging acoustic beam into a pool of fluid (e.g., liquid ink). The angular convergence of this beam is selected so that the beam focuses at or near the free surface of the ink (i.e., at the liquid-air interface). Printing is performed by modulating the radiation pressure that the beam of each ejector exerts against the free surface of ink to selectively eject droplets of ink from the free surface.
FIG. 1 illustrates a schematic of a conventional ejector of a printhead 10 for use in an acoustic ink printer. A transducer 12 and a lens 14 are disposed on opposite sides of a wafer 16. The wafer 16 is preferably formed of a glass. A thin metal plate 18 is spaced vertically from the wafer 16. The metal plate 18 defines an aperture 22. The aperture 22 is disposed adjacent the lens 14 and the transducer 12. A fluid 24, preferably selected from a group including water and aqueous inks, is disposed between the metal plate 18 and the wafer 16. An air space is disposed on the side of the metal plate 18 opposite the fluid 24. An air-fluid interface 26 is disposed at the aperture 22 of the metal plate 18. The fluid 24 wets the edges of the aperture 22. The air-fluid interface 26 is curved (e.g., crescent-shaped) and is commonly referred to as a meniscus.
In the operation of the ejector, the transducer 12 generates an acoustic wave, which propagates through the fluid 24. Dotted lines in FIG. 1 indicate the boundaries of the acoustic wave. The direction in which the acoustic wave propagates is indicated by the arrows 28, 32. The lens 14 focuses the acoustic wave to a spot 34 on the meniscus 26. A droplet 36 is ejected from the aperture 22. The aperture 22 surrounds a region of the droplet formation and helps to constrain the location of the fluid surface. Ideally, as shown in FIG. 1, the droplet 36 is ejected in the direction indicated by arrow 38.
Conventional methods for ejecting a droplet from the meniscus have primarily been directed to insuring the consistent directionality of the ejected droplet. More specifically, it has typically been desirable to eject the droplet along the line defined by the propagating acoustic wave. The propagation direction is illustrated as line 38 in FIG. 1.
A first method for ejecting a droplet along the propagation direction focuses the acoustic wave to a spot on the meniscus that has a tangential plane perpendicular to the propagation direction (see spot 34 in FIG. 1). If acoustic waves of an arbitrary shape are generated, focusing the acoustic wave to such a spot is critical for producing droplets which eject in the propagation direction.
A second method for ejecting a droplet along the propagation direction is disclosed in U.S. Pat. No. 5,808,636 (xe2x80x9cthe ""636 patentxe2x80x9d), which is incorporated herein by reference. The ""636 patent discloses that an ideally shaped acoustic wave produces a droplet that is ejected in the desired direction, regardless of the angle between the acoustic wave and the meniscus. The ideally shaped acoustic wave disclosed in the ""636 patent is about 2 xcexcs.
While the conventional methods for ejecting droplets from the printhead achieve a desired directionality, they also result in at least one drawback. More specifically, because the conventional methods of ejecting droplets from the printhead strive to project the droplets in a single direction, the resolution of the printed output is limited by the spacing of apertures in the printhead.
The present invention provides a new and improved apparatus and method which overcomes the above-referenced problems and others.
An apparatus ejects a droplet of a fluid from a surface of the fluid. An acoustic wave is generated to eject the droplet from an ejection spot on the surface of the fluid. A propagation direction of the acoustic wave is not perpendicular to a plane tangent to the ejection spot. The acoustic wave is shaped into a plurality of tonebursts. An ejection direction of the droplet is a function of the shape of the toneburst.
In accordance with one aspect of the invention, the fluid includes an aqueous ink.
In accordance with another aspect of the invention, a first toneburst causes a first droplet of the fluid to be ejected from the surface in a first ejection direction. The first ejection direction is substantially along the propagation direction of the acoustic wave and is independent of disturbances to the surface of the fluid caused by capillary waves generated by high-speed printing.
In accordance with a more limited aspect of the invention, a second toneburst, having a shape different from the first toneburst, causes a second droplet of the fluid to be ejected from the surface in a second ejection direction. A third toneburst, having a shape different from the first and second tonebursts, causes a third droplet of the fluid to be ejected from the surface in a third ejection direction.
In accordance with another aspect of the invention, the fluid is ejected from an ejector of a printhead of a printer.
In accordance with another aspect of the invention, the fluid is ejected from an ejector of a printhead during high-speed printing.
In accordance with another aspect of the invention, the means for generating the acoustic sound wave includes a piezo-electric element.
In accordance with a more limited aspect of the invention, the acoustic wave is shaped by a Fresnel lens.
One advantage of the present invention is that the resolution of an acoustic ink printhead is increased.
Another advantage of the present invention is that the directionality of droplets ejected from an acoustic ink printhead is controlled by the shape of the acoustic sound wave.
Still further advantages of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiments.